Catalyst and method of manufacture

ABSTRACT

A catalyst system comprising a first catalytic composition comprising a first catalytic material disposed on a metal inorganic support; wherein the metal inorganic support has pores; and at least one promoting metal. The catalyst system further comprises a second catalytic composition comprising, (i) a zeolite, or (ii) a first catalytic material disposed on a first substrate, the first catalytic material comprising an element selected from the group consisting of tungsten, titanium, and vanadium. The catalyst system may further comprise a third catalytic composition. The catalyst system may further comprise a delivery system configured to deliver a reductant and optionally a co-reductant. A catalyst system comprising a first catalytic composition, the second catalytic composition, and the third catalytic composition is also provided. An exhaust system comprising the catalyst systems described herein is also provided.

TECHNICAL FIELD

The systems and techniques described include embodiments that relate tocatalysts. They also include embodiments that relate to the making ofcatalysts and systems that may include catalysts.

DISCUSSION OF RELATED ART

Exhaust streams generated by the combustion of fossil fuels, such as infurnaces, ovens, and engines, contain various potentially undesirablecombustion products including nitrogen oxides (NO_(x)), unburnedhydrocarbons (HC), and carbon monoxide (CO). NO_(x), thoughthermodynamically unstable, may not spontaneously decompose in theabsence of a catalyst. Exhaust streams may employ exhaust treatmentdevices to remove NO_(x) from the exhaust stream.

Examples of exhaust treatment devices include catalytic converters(e.g., three-way catalyst, oxidation catalysts, selective catalyticreduction (SCR) catalysts, and the like), evaporative emissions devices,scrubbing devices (e.g., hydrocarbon (HC), sulfur, and the like),particulate filters/traps, adsorbers/absorbers, plasma reactors (e.g.,non-thermal plasma reactors and thermal plasma reactors), and the like.A three-way catalyst (TWC catalyst) in a catalytic converter may reduceNO_(x) by using CO and residual hydrocarbon. TWC catalysts may beeffective over a specific operating range of both lean and rich fuel/airconditions and within a specific operating temperature range.Particulate catalytic compositions may enable optimization of theconversion of HC, CO, and NO_(x). The conversion rate may depend on theexhaust gas temperature. The catalytic converter may operate at anelevated catalyst temperature of about 300 degrees Celsius or higher.The time period between when the exhaust emissions begin (i.e., “coldstart”), until the time when the substrate heats up to a light-offtemperature, is the light-off time. Light-off temperature is thecatalyst temperature at which fifty percent (50%) of the emissions fromthe engine convert as they pass through the catalyst. Alternativemethods to heat the catalyst may be employed to bring catalysttemperature to the light off temperature.

The exhaust gases from the engine may heat the catalytic converter. Thisheating may help bring the catalyst to the light-off temperature. Theexhaust gases pass through the catalytic converter relatively unchangeduntil the light-off temperature is reached. In addition, the compositionof the engine exhaust gas changes as the engine temperature increasesfrom a cold start temperature to an operating temperature, and the TWCcatalyst may work with the exhaust gas composition that is present atnormal elevated engine operating temperatures.

Selective Catalytic Reduction (SCR) may include a noble metal system,base metal system, or zeolite system. The noble metal catalyst mayoperate in a temperature range of from about 240 degrees Celsius toabout 270 degrees Celsius, but may be inhibited by the presence of SO₂.The base metal catalysts may operate in a temperature range of fromabout 310 degrees Celsius to about 500 degrees Celsius, but may promoteoxidation of SO₂ to SO₃. The zeolites can withstand temperatures up to600 degrees Celsius and, when impregnated with a base metal may have awide range of operating temperatures. SCR systems with ammonia as areductant may yield NO_(x) reduction efficiencies of more than 80percent in large natural gas fired turbine engines and in lean burndiesel engines. However, the presence of ammonia may be undesirable, andthere may be some ammonia slip due to imperfect distribution of reactinggases as well as due to incomplete ammonia consumption. Further, ammoniasolutions require an extra storage tank and are subject to freezing atcold ambient temperatures. SCR of NO_(x) can also be accomplished withhydrocarbons. NO_(x) can be selectively reduced by some organiccompounds (e.g. alkanes, olefins, alcohols) over several catalysts underexcess O₂ conditions. The injection of diesel or methanol has beenexplored in heavy-duty stationary diesel engines to supplement thehydrocarbons (HC) in the exhaust stream. However, the conversionefficiency may be reduced outside the temperature range of 300 degreesCelsius to 400 degrees Celsius. In addition, this technique may haveHC-slip over the catalyst, transportation and on-site bulk storage ofhydrocarbons, and possible atmospheric release of the HC. The partialoxidation of hydrocarbons may release CO, unburned HC, and particulates.

It may be desirable to have a catalyst that can effect emissionreduction across a range of temperatures and operating conditions thatdiffer from those currently available. It may also be desirable to havea catalyst that can effect NO_(x) reduction using a reductant that isdifferent than the currently used reductants.

BRIEF DESCRIPTION

In one embodiment, a catalyst system is provided. The catalyst systemcomprises a first catalytic composition comprising a homogeneous solidmixture containing at least one catalytic metal and at least one metalinorganic support; wherein the pores of the solid mixture have anaverage diameter in a range of about 1 nanometer to about 15 nanometers;and at least one promoting metal. The catalyst system further comprisesa second catalytic composition comprising, (i) a zeolite, or (ii) afirst catalytic material disposed on a first substrate, the firstcatalytic material comprising an element selected from the groupconsisting of tungsten, titanium, and vanadium.

In another embodiment, a catalyst system is provided. The catalystsystem comprises a first catalytic composition comprising, a homogeneoussolid mixture containing at least one catalytic metal and at least onemetal inorganic support; wherein the pores of the solid mixture have anaverage diameter in a range of about 1 nanometer to about 15 nanometers;and at least one promoting metal. The catalyst system further comprisesa second catalytic composition comprising, (i) a zeolite, or (ii) afirst catalytic material disposed on a first substrate, the firstcatalytic material comprising an element selected from the groupconsisting of tungsten, titanium, and vanadium. The catalyst system alsocomprises a third catalytic composition disposed downstream from thesecond catalytic composition; the third catalytic composition comprisinga second catalytic material disposed on a second substrate, wherein thesecond catalytic material is selected from the group consisting ofplatinum, palladium, ruthenium, rubidium, osmium, and iridium.

In yet another embodiment, a catalyst system is provided. The catalystsystem comprises a first catalytic composition comprising, a firstcatalytic material comprising silver disposed on a first substrate, andat least one promoting metal. The catalyst system further comprises asecond catalytic composition comprising, (i) a zeolite, or (ii) a secondcatalytic material disposed on a second substrate, the second catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium. The catalyst system also comprises athird catalytic composition disposed downstream from the secondcatalytic composition; the third catalytic composition comprising athird catalytic material disposed on a third substrate, wherein thethird catalytic material is selected from the group consisting ofplatinum, palladium, ruthenium, rubidium, osmium, and iridium.

In still yet another embodiment, is provided an exhaust systemcomprising, a fuel delivery system configured to deliver a fuel to anengine; an exhaust stream path configured to receive an exhaust streamfrom the engine; a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a firstcatalytic composition comprising, a homogeneous solid mixture containingat least one catalytic metal and at least one metal inorganic support;wherein the pores of the solid mixture have an average diameter in arange of about 1 nanometer to about 15 nanometers; and at least onepromoting metal. The catalyst system further comprises a secondcatalytic composition comprising, (i) a zeolite, or (ii) a firstcatalytic material disposed on a first substrate, the first catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium.

In still yet another embodiment, is provided an exhaust systemcomprising, a fuel delivery system configured to deliver a fuel to anengine; an exhaust stream path configured to receive an exhaust streamfrom the engine; and a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a firstcatalytic composition comprising, a homogeneous solid mixture containingat least one catalytic metal and at least one metal inorganic support;wherein the pores of the solid mixture have an average diameter in arange of about 1 nanometer to about 15 nanometers; and at least onepromoting metal. The catalyst system further comprises a secondcatalytic composition comprising, (i) a zeolite, or (ii) a firstcatalytic material disposed on a first substrate, the first catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium. The catalyst further comprises a thirdcatalytic composition disposed downstream from the second catalyticcomposition; the third catalytic composition comprising a secondcatalytic material disposed on a second substrate, wherein the secondcatalytic material is selected from the group consisting of platinum,palladium, ruthenium, rubidium, osmium, and iridium.

In still yet another embodiment, is provided an exhaust systemcomprising, a fuel delivery system configured to deliver a fuel to anengine; an exhaust stream path configured to receive an exhaust streamfrom the engine; and a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a firstcatalytic composition comprising, a first catalytic material comprisingsilver disposed on a first substrate, and at least one promoting metal.The catalyst system further comprises a second catalytic compositioncomprising, (i) a zeolite, or (ii) a second catalytic material disposedon a second substrate, the second catalytic material comprising anelement selected from the group consisting of tungsten, titanium, andvanadium. The catalyst further comprises a third catalytic compositiondisposed downstream from the second catalytic composition; the thirdcatalytic composition comprising a third catalytic material disposed ona third substrate, wherein the third catalytic material is selected fromthe group consisting of platinum, palladium, ruthenium, rubidium,osmium, and iridium.

BRIEF DESCRIPTION OF DRAWING FIGURES

FIG. 1 is a schematic diagram depicting a catalyst system set-up in afurnace;

FIG. 2 is a schematic diagram depicting a catalyst system set-up in afurnace in accordance with an embodiment of the invention;

FIG. 3 is a schematic diagram depicting a catalyst system set-up in afurnace in accordance with an embodiment of the invention;

FIG. 4 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention;

FIG. 5 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention;

FIG. 6 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention;

FIG. 7 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention;

FIG. 8 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention; and

FIG. 9 is a schematic diagram depicting an exhaust system comprising thecatalyst system set-up in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

The systems and techniques described include embodiments that relate tocatalysts and their use and manufacture. Other embodiments relate toarticles that include catalysts and catalytic compositions that maychemically reduce NO_(x) that is present in emissions generated duringcombustion, for example in furnaces, ovens, engines, and locomotives.

Embodiments of the invention described herein address the notedshortcomings of the state of the art. The catalyst system describedherein fills the needs described above by employing a multiple bedcatalyst system comprising at least a first catalytic composition and asecond catalytic composition to reduce the NO_(x) in an exhaust gas. Thefirst catalytic composition uses a homogeneous solid mixture containingat least one catalytic metal and at least one metal inorganic support;wherein the pores of the solid mixture have an average diameter in arange of about 1 nanometer to about 15 nanometers; and at least onepromoting metal. The first catalytic composition produces nitrogencontaining chemicals such as ammonia. The second catalytic compositioncomprises either a first catalytic material disposed on a firstsubstrate or a zeolite, which may use the ammonia or ammonia likeproducts generated by the first catalytic composition as a NO_(x)reductant to further reduce additional NO_(x) in the exhaust gas. Thecatalyst system may further include a third catalytic composition usedto oxidize any unwanted products of reaction or unused reactants orreductants. In certain embodiments, the catalyst system may include afirst catalytic composition a first catalytic material comprising silverdisposed on a first substrate, and at least one promoting metal, asecond catalytic composition, and a third catalytic composition, whichin combination reduce NO_(x) in the exhaust gas. The first catalyticcomposition may include a first catalytic material disposed on a firstsubstrate. The second catalytic composition may include a secondcatalytic material disposed on a second substrate. The third catalyticcomposition may include a third catalytic material disposed on a thirdsubstrate. The catalyst systems described herein further employ ahydrocarbon reductant, such as for example diesel. One advantage ofusing diesel as a reductant is that it is readily available on boardvehicles with diesel engines. In certain embodiments, a co-reductant maybe used with hydrocarbon reductant to lower the light off temperature ofthe catalyst.

A catalyst is a substance that can cause a change in the rate of achemical reaction without itself being consumed in the reaction. Aslurry is a mixture of a liquid and finely divided particles. A sol is acolloidal solution. A powder is a substance including finely dividedsolid particles. A monolith may be a ceramic block having a number ofchannels, and may be made by extrusion of clay, binders and additivesthat are pushed through a dye to create a structure. Approximatinglanguage, as used herein throughout the specification and claims, may beapplied to modify any quantitative representation that could permissiblyvary without resulting in a change in the basic function to which it isrelated. Accordingly, a value modified by a term such as “about” is notto be limited to the precise value specified. In some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. Similarly, “free” may be used in combinationwith a term, and may include an insubstantial number, or trace amounts,while still being considered free of the modified term.

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Moreover, the use of “top,” “bottom,” “above,” “below,” and variationsof these terms is made for convenience, but does not require anyparticular orientation of the components unless otherwise stated. Asused herein, the terms “disposed on” or “deposited over” or “disposedbetween” refers to both secured or disposed directly in contact with andindirectly by having intervening layers therebetween.

In one embodiment, a catalyst system is provided. The catalyst systemcomprises a first catalytic composition comprising a homogeneous solidmixture containing silver and one metal inorganic support; wherein thepores of the solid mixture have an average diameter in a range of about1 nanometer to about 15 nanometers; and at least one promoting metal.The catalyst system further comprises a second catalytic compositioncomprising, (i) a zeolite, or (ii) a first catalytic material disposedon a first substrate, the first catalytic material comprising an elementselected from the group consisting of tungsten, titanium, and vanadium.

In one embodiment, the catalytic metal may include alkali metals,alkaline earth metals, and transition metals. Suitable transition metalsthat may be used as the catalytic metal may include silver, platinum,gold, palladium, iron, nickel, cobalt, gallium, indium, ruthenium,rhodium, osmium, iridium, or combinations of at least two of theforegoing metals. In one embodiment, the catlaytic metal is selectedfrom one or more of gallium, indium, and silver. In one embodiment, thecatalytic metal is silver.

In one embodiment, the metal inorganic support has pores. The porousmetal inorganic support is a reaction product of a reactive solution, asolvent, a modifier and a templating agent. A method includes mixing areactive solution and a templating agent to form a gel; and calciningthe gel to form a porous metal inorganic support that is capable ofsupporting a catalyst composition. The metal inorganic support may bemanufactured via a process, as described in co-pending U.S. PatentApplication 20090074641 which is incorporated herein in its entirety. Asused herein, without further qualifiers, porous refers to a materialcontaining pores with diameters in a range of from about 1 nanometer toabout 15 nanometers.

In one embodiment, the average pore size of the metal inorganic supportis controlled and selected to reduce or eliminate poisoning. Poisoningmay affect catalytic ability, and may be by aromatic species present inthe reductant or in the exhaust gas stream. The porous materialdescribed herein is more resistant to poisoning from an aromaticcontaining reductant than a baseline typical gamma phase aluminaimpregnated with silver.

In various embodiments, the catalytic metal may be present in the firstcatalytic composition in an amount greater than about 0.25 mole percent.One skilled in the art will appreciate that the amount selection may bebased on end use parameters, economic considerations, desired efficacy,and the like. In one embodiment, the amount of the catalytic metalpresent in the first catalytic composition is in a range of from about0.25 mole percent to about 10 mole percent. In another embodiment, theamount of the catalytic metal present in the first catalytic compositionis in a range of from about 0.5 mole percent to about 9 mole percent. Inyet another embodiment, the amount of the catalytic metal present in thefirst catalytic composition is in a range of from about 1 mole percentto about 8 mole percent. In one embodiment, the amount of catalyticmetal in the first catalytic composition is about 1.5 mole percent toabout 6 mole percent.

In one embodiment, the metal inorganic support may include an inorganicmaterial. As used herein, the phrase “metal inorganic support” means asupport that comprises an inorganic material, which material in partcontains atoms or cations of one or more of the metal elements. Suitableinorganic materials may include, for example, oxides, carbides,nitrides, hydroxides, oxides, carbonitrides, oxynitrides, borides, orborocarbides. In one embodiment, the inorganic oxide may have hydroxidecoatings. In one embodiment, the inorganic oxide may be a metal oxide.The metal oxide may have a hydroxide coating. Other suitable metalinorganics may include one or more metal carbides, metal nitrides, metalhydroxides, metal carbonitrides, metal oxynitrides, metal borides, ormetal borocarbides. Metal cations used in the foregoing inorganicmaterials can be transition metals, alkali metals, alkaline earthmetals, rare earth metals, or the like.

Examples of suitable inorganic oxides include silica (SiO₂), alumina(Al₂O₃), titania (TiO₂), zirconia (ZrO₂), ceria (CeO₂), manganese oxide(MnO₂), zinc oxide (ZnO), iron oxides (for example, FeO, beta-Fe₂O₃,gamma-Fe₂O₃, beta-Fe₂O₃, Fe₃O₄, or the like), calcium oxide (CaO), andmanganese dioxide (MnO2 and Mn₃O₄). Examples of suitable inorganiccarbides include silicon carbide (SiC), titanium carbide (TiC), tantalumcarbide (TaC), tungsten carbide (WC), hafnium carbide (HfC), or thelike. Examples of suitable nitrides include silicon nitrides (Si₃N₄),titanium nitride (TiN), or the like. Examples of suitable boridesinclude lanthanum boride (LaB₆), chromium borides (CrB and CrB₂),molybdenum borides (MoB₂, Mo₂B₅ and MoB), tungsten boride (W₂B₅), or thelike. In one embodiment, the inorganic substrate is alumina. The aluminaemployed may be crystalline or amorphous. In one embodiment, the porousmetal inorganic support comprises porous alumina and the catalytic metalcomprises silver.

In one embodiment, the metal inorganic support has a mean pore sizegreater than about 0.5 nanometers. In one embodiment, the metalinorganic support may have an average diameter of pores in a range ofabout 1 nanometer to about 15 nanometers. In another embodiment, themetal inorganic support may have an average diameter of pores in a rangeof about 2 nanometers to about 12 nanometers. In yet another embodiment,the metal inorganic support may have an average diameter of pores in arange of about 3 nanometers to about 15 nanometers. In one embodiment,the metal inorganic support may have an average diameter of pores in arange of about 1 nanometer to about 5 nanometers. The average diameterof pores may be measured using nitrogen adsorption measurements with BETmethod. BET theory is a rule for the physical adsorption of gasmolecules on a solid surface and serves as the basis for an importantanalysis technique for the measurement of the specific surface area of amaterial. BET is short hand for the inventors' names: Stephen Brunauer,Paul Hugh Emmett, and Edward Teller, who developed the theory.

In certain embodiments, the pore size has a narrow monomodaldistribution. In one embodiment, the pores have a pore size distributionpolydispersity index that is less than about 1.5, less than about 1.3,or less than about 1.1. In one embodiment, the distribution of diametersizes may be bimodal, or multimodal.

In another embodiment, the porous metal inorganic support includes oneor more stabilizers, which may be added to the metal inorganic support.For example, in various embodiments, the metal inorganic supportcomprising predominantly alumina has smaller amounts of yttria,zirconia, or ceria added to it. In one embodiment, the amount of yttria,zirconia, or ceria is in a range of about 0.1 percent to about 10percent based on the weight of the alumina. In another embodiment, theamount of yttria, zirconia, or ceria is in a range of about 1 percent toabout 9 percent based on the weight of the alumina. In yet anotherembodiment, the amount of yttria, zirconia, or ceria is in a range ofabout 2 percent to about 6 percent based on the weight of the alumina.

In one embodiment, the pores may be distributed in a controlled andrepeating fashion to form a pattern. In another embodiment, the porearrangement is regular and not random. As defined herein, the phrase“pore arrangement is regular” means that the pores may be ordered andmay have an average periodicity. The average pore spacing may becontrolled and selected based on the surfactant selection that is usedduring the gelation. In one embodiment, the pores are unidirectional,are periodically spaced, and have an average periodicity. One porousmetal inorganic support has pores that have a spacing of greater thanabout 20 Angstroms. In one embodiment, the spacing is in a range of fromabout 30 Angstroms to about 300 Angstroms. In another embodiment, thespacing is in a range of from about 50 Angstroms to about 200 Angstroms.In yet another embodiment, the spacing is in a range of from about 60Angstroms to about 150 Angstroms. The average pore spacing (periodicity)may be measured using small angle X-ray scattering. In anotherembodiment, the pore spacing is random.

The porous metal inorganic support may have a surface area greater thanabout 50 square meters per gram. In one embodiment, the porous metalinorganic support has a surface area that is in a range of from about 50square meters per gram to about 2000 square meters per gram. In anotherembodiment, the porous metal inorganic support has a surface area thatis in a range of from about 100 square meters per gram to about 1000square meters per gram. In one embodiment, the porous metal inorganicsupport has a surface area that is in a range of from about 300 squaremeters per gram to about 600 square meters per gram.

The porous metal inorganic support may be present in the first catalyticcomposition in an amount that is greater than about 50 mole percentbased on the catalyst system. In one embodiment, the amount present isin a range of from about 50 mole percent to about 99 mole percent of thefirst catalytic composition based on the catalyst system. In anotherembodiment, the amount present is in a range of from about 55 molepercent to about 89 mole percent of the first catalytic compositionbased on the catalyst system. In yet another embodiment, the amountpresent is in a range of from about 60 mole percent to about 79 molepercent of the first catalytic composition based on the catalyst system.In one embodiment, the amount present is in a range of from about 94mole percent to about 99 mole percent of the first catalytic compositionbased on the catalyst system.

The porous metal inorganic support may be made up of particles. Theparticles may be agglomerates, a sintered mass, a surface coating on asupport, or the like. The porous metal inorganic support may have anaverage particle size of up to about 4 millimeters. In one embodiment,the porous inorganic materials may have an average particle size in arange of from about 5 micrometers to about 3 millimeters. In anotherembodiment, the porous inorganic materials may have an average particlesize in a range of from about 500 micrometers to about 2.5 millimeters.In yet another embodiment, the porous inorganic materials may have anaverage particle size in a range of from about 1 millimeter to about 2millimeters. In an exemplary embodiment, the porous substrate has anaverage particle size of about 40 micrometers.

The first catalytic composition may be present in an amount of up toabout 90 weight percent, based upon the total weight of the catalystsystem. In one embodiment, the first catalytic composition may bepresent in an amount in a range of from about 1 weight percent to about90 weight percent, based upon the total weight of the catalyst system.In another embodiment, the first catalytic composition in the form of abed may be present in an amount in a range of from about 20 weightpercent to about 80 weight percent, based upon the total weight of thecatalyst system. In yet another embodiment the first catalyticcomposition may be present in an amount in a range of from about 50weight percent to about 70 weight percent, based upon the total weightof the catalyst system. In various embodiments, the ratio is determinedby the quantity of species generated on the first bed that are utilizedon the second bed. This will depend on several variables specific to theparticular exhaust application where the catalyst system may beemployed. The type of engine or turbine, the exhaust temperature, theflow rate, concentration of NO_(x), etc. all factor into determining theratio of the first catalytic composition to the second catalyticcomposition. The ratio can be optimized for a particular application ina way such as to achieve the highest NO_(x) conversion in a givensystem.

In one embodiment, the first catalytic composition comprises at leastone promoting metal. A promoting metal is a metal that enhances theaction of a catalyst. In one embodiment, the promoting metal may beselected from the group consisting of gallium, indium, gold, vanadium,zinc, tin, bismuth, cobalt, molybdenum, and tungsten. In one embodiment,the promoting metal may be present in an amount in a range of from about0.1 weight percent to about 20 weight percent, based upon the totalweight of the catalyst system. In another embodiment, the firstcatalytic composition may be present in an amount in a range of fromabout 0.5 weight percent to about 15 weight percent, based upon thetotal weight of the catalyst system. In yet another embodiment, thefirst catalytic composition may be present in an amount in a range offrom about 1 weight percent to about 12 weight percent, based upon thetotal weight of the catalyst system.

In one embodiment, the second catalytic composition may include azeolite. The function of the first catalytic material includes the useof ammonia or ammonia like products generated by the first catalyticcomposition as a NO_(x) reductant to further reduce additional NO_(x) inthe exhaust gas. In one embodiment, the zeolite is free of additionalmetals, i.e., the aluminum and silicon metal ions in the zeolite are notexchanged with any other metal ions, for example, iron or copper ions.The zeolites may be naturally occurring or synthetic. Examples ofsuitable zeolites are zeolite Y, zeolite beta, ferrierite, mordenite,ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50,ZSM-57, zeolite A, zeolite X, or a combination comprising at least twoof the foregoing zeolites. In one embodiment, the first catalyticmaterial consists essentially of ferrierite. An exemplary zeolite is aferrierite having a silicon to aluminum ratio of from about 10 to about30. In another embodiment, the ferrierite has a silicon to aluminumratio of from about 12 to about 25. In yet another embodiment, theferrierite has a silicon to aluminum ratio of from about 15 to about 20.In one embodiment, the zeolite includes additional metals, i.e., thealuminum and silicon metal ions in the zeolite are exchanged with anyother metal ions, for example, iron or copper ions. Examples of such ionexchanged zeolites include iron zeolite and copper zeolite.

Examples of commercially available zeolites that may be used in thesecond catalytic composition are marketed under the followingtrademarks: CBV100, CBV300, CBV400, CBV500, CBV600, CBV712, CBV720,CBV760, CBV780, CBV901, CP814E, CP814C, CP811C-300, CP914, CP914C,CBV2314, CBV3024E, CBV5524G, CBV8014, CBV28014, CBV10A, CBV21A, CBV90A,or the like, or a combination including at least two of the foregoingcommercially available zeolites.

The zeolite particles may be in the form of extrudates and generallyhave an average particle size of up to about 2 millimeters. In oneembodiment, the zeolite particles have an average particle size of fromabout 0.001 millimeters to about 1.1 millimeters. In another embodiment,the zeolite particles have an average particle size of from about 0.1millimeters to about 0.9 millimeters. In yet another embodiment, thezeolite particles have an average particle size of from about 0.2millimeters to about 0.8 millimeters. In an exemplary embodiment, thezeolite particles have an average particle size of about 0.001millimeter.

The zeolite particles may have a surface area of up to about 600 squaremeters per gram. In one embodiment, the zeolite particles may have asurface area in a range of from about 50 square meters per gram to about600 square meters per gram. In another embodiment, the zeolite particlesmay have a surface area in a range of from about 80 square meters pergram to about 500 square meters per gram. In yet another embodiment, thezeolite particles may have a surface area in a range of from about 100square meters per gram to about 400 square meters per gram. A highspecific surface area typically results in more efficient conversion inaddition to other factors including unit cell sizes, pore sizes, type ofcatalytic material, and exchanged metals.

In another embodiment, the second catalytic composition includes a firstcatalytic material disposed upon a first substrate. Suitable materialsthat may be employed as the first substrate include the inorganicmaterials described above for the metal inorganic support. The firstcatalytic material may include an element selected from the groupconsisting of tungsten, titanium, and vanadium.

The first catalytic material may be present in the second catalyticcomposition in an amount up to about 50 mole percent based on the amountof the catalyst system. In one embodiment, the first catalytic materialis present in the second catalytic composition in an amount in a rangeof from about 0.025 mole percent to about 50 mole percent based on theamount of the catalyst system. In another embodiment, the firstcatalytic material is present in the second catalytic composition in anamount in a range of from about 0.5 mole percent to about 40 molepercent based on the amount of the catalyst system. In yet anotherembodiment, the first catalytic material is present in the secondcatalytic composition in an amount in a range of from about 1.0 molepercent to about 30 mole percent based on the amount of the catalystsystem. In one embodiment, the amount of first catalytic material in thesecond catalytic composition is about 1.5 mole percent based on theamount of the catalyst system. In another embodiment, the amount offirst catalytic material in the second catalytic composition is about 5mole percent based on the amount of the catalyst system.

The second catalytic composition may be used in an amount of up to about80 weight percent, based upon the total weight of the catalyst system.In one embodiment, the second catalytic composition may be used in anamount in a range of from about 20 weight percent to about 70 weightpercent based upon the total weight of the catalyst system. In anotherembodiment, the second catalytic composition may be used in an amount ina range of from about 30 weight percent to about 60 weight percent basedupon the total weight of the catalyst system. In yet another embodiment,the second catalytic composition may be used in an amount in a range offrom about 40 weight percent to about 50 weight percent based upon thetotal weight of the catalyst system. Also the first catalytic materialmay be present in the second catalytic composition in an amount selectedfrom the same range amount of the catalytic material in the metalinorganic support as described for the first catalytic compositionabove.

In one embodiment, the catalyst system further comprises a thirdcatalytic composition disposed downstream from the second catalyticcomposition; the third catalytic composition comprising a secondcatalytic material disposed on a second substrate, wherein the secondcatalytic material is selected from the group consisting of platinum,palladium, ruthenium, rhodium, osmium, and iridium. Suitable materialsthat may be employed as the second substrate include the inorganicmaterials described above for the metal inorganic support. The secondcatalytic material is typically used to oxidize any unwanted products ofreaction or unused reactants or reductants.

In one embodiment, the third catalytic composition is a diesel oxidationcatalyst (DOC). A DOC is a flow through device that consists of acanister containing a honeycomb-like structure or substrate. The secondsubstrate has a large surface area that is coated with an activecatalyst layer. This layer contains a small, well dispersed amount ofprecious metals such as platinum or palladium. As the exhaust gasestraverse the DOC, carbon monoxide, gaseous hydrocarbons and liquidhydrocarbon particles (unburned fuel and oil) are oxidized, therebyreducing harmful emissions.

The second catalytic material may be present in the third catalyticcomposition in an amount up to about 50 mole percent. In one embodiment,the second catalytic material is present in the third catalyticcomposition in an amount in a range of from about 0.025 mole percent toabout 50 mole percent. In another embodiment, the second catalyticmaterial is present in the third catalytic composition in an amount in arange of from about 0.5 mole percent to about 40 mole percent. In yetanother embodiment, the second catalytic material is present in thethird catalytic composition in an amount in a range of from about 1.0mole percent to about 30 mole percent. In one embodiment, the amount ofsecond catalytic material in the third catalytic composition is about1.5 mole percent. In another embodiment, the amount of second catalyticmaterial in the third catalytic composition is about 5 mole percent.

The third catalytic composition may be used in an amount of up to about90 weight percent, based upon the total weight of the catalyst system.In one embodiment, the third catalytic composition may be used in anamount in a range of from about 10 weight percent to about 80 weightpercent based upon the total weight of the catalyst system. In anotherembodiment, the third catalytic composition may be used in an amount ina range of from about 20 weight percent to about 70 weight percent basedupon the total weight of the catalyst system. In yet another embodiment,the third catalytic composition may be used in an amount in a range offrom about 30 weight percent to about 60 weight percent based upon thetotal weight of the catalyst system.

In one embodiment, the second substrate may include an inorganicmaterial. In one embodiment, the inorganic materials may include thematerials listed above for the metal inorganic support. Suitablematerials that may be employed as the second substrate include at leastone member selected from the group consisting of alumina, titania,zirconia, ceria, silicon carbide and mixtures thereof.

In one embodiment, the catalyst system further comprises a deliverysystem configured to deliver a reductant. When the catalytic compositionis employed to reduce NO_(x) generated in emissions from furnaces,ovens, locomotives and engines, a variety of hydrocarbons may beeffectively used as a reductant. In one embodiment, the reductant is ahydrocarbon. In one embodiment, the hydrocarbon has an average carbonchain length in the range of about 2 carbon atoms to about 24 carbonatoms. In one embodiment, the reductant is one or more of diesel,ultra-low sulfur diesel, ethanol, gasoline, and octane. In oneembodiment, the reductant is a hydrocarbon having an average carbonchain length in the range of about 3 carbon atoms or less. In oneembodiment, the reductant is one or more of methane, ethylene, andpropylene. In one embodiment, the reductant is an oxygenatedhydrocarbon. In one embodiment, the oxygenated hydrocarbon is ethanol.

In certain embodiments, a co-reductant may be used with hydrocarbonreductant to lower the light off temperature of the catalyst. In oneembodiment, the co-reductant is hydrogen. In one embodiment, the amountof co-reductant employed may be in a range of from about 0 parts permillion to about 4000 parts per million based on the total volumeticflow rate of the exhaust. In another embodiment, the amount ofco-reductant employed may be in a range of from about 10 parts permillion to about 3000 parts per million based on the total volumeticflow rate of the exhaust. In yet another embodiment, the amount ofco-reductant employed may be in a range of from about 20 parts permillion to about 2000 parts per million based on the total volumeticflow rate of the exhaust. In one embodiment, the amount of co-reductantemployed may be in a range of from about 0 parts per million to about1000 parts per million based on the total volumetic flow rate of theexhaust.

In an exemplary embodiment, diesel can be used as a reductant. Thecatalytic composition can reduce NO_(x) while using higher hydrocarbonshaving from about 5 to about 9 carbon atoms per molecule as a reductant.The catalyst system advantageously functions across a variety oftemperature ranges. Suitable temperature ranges may include temperaturesof greater than about 325 degrees Celsius. Other temperature ranges mayinclude those up to about 400 degrees Celsius.

In another embodiment, a catalyst system is provided. The catalystsystem comprises a first catalytic composition comprising a homogeneoussolid mixture containing silver and one metal inorganic support; whereinthe pores of the solid mixture have an average diameter in a range ofabout 1 nanometer to about 15 nanometers; and at least one promotingmetal. The catalyst system further comprises a second catalyticcomposition comprising, (i) a zeolite, or (ii) a first catalyticmaterial disposed on a first substrate, the first catalytic materialcomprising an element selected from the group consisting of tungsten,titanium, and vanadium. The catalyst system also comprises a thirdcatalytic composition disposed downstream from the second catalyticcomposition; the third catalytic composition comprising a secondcatalytic material disposed on a second substrate, wherein the thirdcatalytic material is selected from the group consisting of platinum,palladium, ruthenium, rubidium, osmium, and iridium.

In yet another embodiment, a catalyst system is provided. The catalystsystem comprises a first catalytic composition comprising, a firstcatalytic material comprising silver disposed on a first substrate, andat least one promoting metal. The catalyst system further comprises asecond catalytic composition comprising, (i) a zeolite, or (ii) a secondcatalytic material disposed on a second substrate, the second catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium. The catalyst system also comprises athird catalytic composition disposed downstream from the secondcatalytic composition; the third catalytic composition comprising athird catalytic material disposed on a third substrate, wherein thethird catalytic material is selected from the group consisting ofplatinum, palladium, ruthenium, rubidium, osmium, and iridium.

Suitable materials that may be employed as the first substrate includethe inorganic materials selected from the group consisting of alumina,titania, zirconia, ceria, silicon carbide and mixtures thereof. Thepromoting materials employed may be the same as described above. Thefirst catalytic material may be present in the first catalyticcomposition in an amount up to about 50 mole percent. In one embodiment,the first catalytic material is present in the first catalyticcomposition in an amount in a range of from about 0.025 mole percent toabout 50 mole percent. In another embodiment, the first catalyticmaterial is present in the first catalytic composition in an amount in arange of from about 0.5 mole percent to about 40 mole percent. In yetanother embodiment, the first catalytic material is present in the firstcatalytic composition in an amount in a range of from about 1.0 molepercent to about 30 mole percent. In one embodiment, the amount of firstcatalytic material in the first catalytic composition is about 1.5 molepercent. In another embodiment, the amount of first catalytic materialin the first catalytic composition is about 5 mole percent.

In one embodiment, the first catalytic composition may be used in anamount of up to about 90 weight percent, based upon the total weight ofthe catalyst system. In one embodiment, the first catalytic compositionmay be used in an amount in a range of from about 10 weight percent toabout 80 weight percent based upon the total weight of the catalystsystem. In another embodiment, the first catalytic composition may beused in an amount in a range of from about 20 weight percent to about 70weight percent based upon the total weight of the catalyst system. Inyet another embodiment, the first catalytic composition may be used inan amount in a range of from about 30 weight percent to about 60 weightpercent based upon the total weight of the catalyst system.

In one embodiment, the second catalytic material comprises a zeolite.The function of the second catalytic material includes the use ofammonia or ammonia like products generated by the first catalyticcomposition as a NO_(x) reductant to further reduce additional NO_(x) inthe exhaust gas. Suitable zeolites may be selected from the zeolitesdiscussed above for the first catalytic material of the second catalyticcomposition. In another embodiment, the second catalytic compositionincludes a second catalytic material disposed upon a second substrate.Suitable materials that may be employed as the second substrate includethe inorganic materials described above for the metal inorganic support.The second catalytic material may include an element selected from thegroup consisting of tungsten, titanium, and vanadium.

The second catalytic material may be present in the second catalyticcomposition in an amount up to about 50 mole percent based on the amountof the catalyst system. In one embodiment, the second catalytic materialis present in the second catalytic composition in an amount in a rangeof from about 0.025 mole percent to about 50 mole percent based on theamount of the catalyst system. In another embodiment, the secondcatalytic material is present in the second catalytic composition in anamount in a range of from about 0.5 mole percent to about 40 molepercent based on the amount of the catalyst system. In yet anotherembodiment, the second catalytic material is present in the secondcatalytic composition in an amount in a range of from about 1.0 molepercent to about 30 mole percent based on the amount of the catalystsystem. In one embodiment, the amount of second catalytic material inthe second catalytic composition is about 1.5 mole percent based on theamount of the catalyst system. In another embodiment, the amount ofsecond catalytic material in the second catalytic composition is about 5mole percent based on the amount of the catalyst system.

The second catalytic composition may be used in an amount of up to about80 weight percent, based upon the total weight of the catalyst system.In one embodiment, the second catalytic composition may be used in anamount in a range of from about 20 weight percent to about 70 weightpercent based upon the total weight of the catalyst system. In anotherembodiment, the second catalytic composition may be used in an amount ina range of from about 30 weight percent to about 60 weight percent basedupon the total weight of the catalyst system. In yet another embodiment,the second catalytic composition may be used in an amount in a range offrom about 40 weight percent to about 50 weight percent based upon thetotal weight of the catalyst system.

In one embodiment, the catalyst system further comprises a thirdcatalytic composition disposed downstream from the second catalyticcomposition; the third catalytic composition comprising a thirdcatalytic material disposed on a third substrate, wherein the thirdcatalytic material is selected from the group consisting of platinum,palladium, ruthenium, rhodium, osmium, and iridium. Suitable materialsthat may be employed as the third substrate include the inorganicmaterials described above for the metal inorganic support. The thirdcatalytic material is typically used to oxidize any unwanted products ofreaction or unused reactants or reductants. In one embodiment, the thirdcatalytic composition is a diesel oxidation catalyst (DOC).

The third catalytic material may be present in the third catalyticcomposition in an amount up to about 50 mole percent. In one embodiment,the third catalytic material is present in the third catalyticcomposition in an amount in a range of from about 0.025 mole percent toabout 50 mole percent. In another embodiment, the third catalyticmaterial is present in the third catalytic composition in an amount in arange of from about 0.5 mole percent to about 40 mole percent. In yetanother embodiment, the third catalytic material is present in the thirdcatalytic composition in an amount in a range of from about 1.0 molepercent to about 30 mole percent. In one embodiment, the amount of thirdcatalytic material in the third catalytic composition is about 1.5 molepercent. In another embodiment, the amount of third catalytic materialin the third catalytic composition is about 5 mole percent.

The third catalytic composition may be used in an amount of up to about90 weight percent, based upon the total weight of the catalyst system.In one embodiment, the third catalytic composition may be used in anamount in a range of from about 10 weight percent to about 80 weightpercent based upon the total weight of the catalyst system. In anotherembodiment, the third catalytic composition may be used in an amount ina range of from about 20 weight percent to about 70 weight percent basedupon the total weight of the catalyst system. In yet another embodiment,the third catalytic composition may be used in an amount in a range offrom about 30 weight percent to about 60 weight percent based upon thetotal weight of the catalyst system.

In one embodiment, the third substrate may include an inorganicmaterial. In one embodiment, the inorganic materials may include thematerials listed above for the metal inorganic support. Suitablematerials that may be employed as the third substrate include at leastone member selected from the group consisting of alumina, titania,zirconia, ceria, silicon carbide and mixtures thereof.

In a method of using the catalyst system, the catalyst system isdisposed in the exhaust stream of an internal combustion engine. Theinternal combustion engine may be part of any of a variety of mobile orfixed assets, for example, an automobile, locomotive, or powergenerator. Because different engines have different combustioncharacteristics, the exhaust stream components differ from one system toanother. Such differences may include variations in NO_(x) levels,presence of sulfur, and the presence or quantity of other species ofreaction product. Changes in the operating parameters of the engine mayalso alter the exhaust flow characteristics. Examples of differingoperating parameters may include temperature and flow rate. The catalystmay be used to reduce NO_(x) to nitrogen and oxygen at a desirable rateand at a desirable temperature appropriate for the given system andoperating parameters. The catalyst system may be disposed in the exhaustgas path in any of a variety of ways, for example, in powdered form, inthe form of an extruded monolith, or as a washcoated substrate. Varioustechniques for creating such powder beds, extrudates, or coatedsubstrates are known in the art, and may be applied as appropriate forthe desired composition and catalyst form. Further, each of thecatalytic compostions may be supported separately or on the samesupport. They could even overlap or be partially mixed.

During operation, the catalyst system can convert the NO_(x) present inan exhaust stream by about 90 weight percent. In one embodiment, thecatalyst system can convert the NO_(x) present in an exhaust stream inan amount in a range of from about 10 weight percent to about 90 weightpercent based on the weight of the exhaust stream. In anotherembodiment, the catalyst system can convert the NO_(x) present in anexhaust stream in an amount in a range of from about 20 weight percentto about 80 weight percent based on the weight of the exhaust stream. Inyet another embodiment, the catalyst system can convert the NO_(x)present in an exhaust stream in an amount in a range of from about 30weight percent to about 70 weight percent based on the weight of theexhaust stream.

EXAMPLES

The following examples illustrate methods and embodiments in accordancewith exemplary embodiments, and as such should not be construed asimposing limitations upon the claims. All components are commerciallyavailable from common chemical suppliers. The component and the sourceare listed in Table 1 given below.

TABLE 1 Component Source ethylacetoacetate Aldrich triton X114 Aldrichaluminum (sec- Gelest butoxide)₃ silver nitrate GFS chemicals isopropylalcohol EM Scientific iron-zeolite and Umicore copper-zeolite

Example 1 Preparation of Porous Alumina with Silver

A 100 gallon reactor equipped with a stirrer was charged with: isopropylalcohol (72 kilograms), ethylacetoacetate (936 grams), triton X114 (3.12kilograms) and Aluminum (sec-butoxide)₃ (18 kilograms). The resultantmixture was stirred for about 30 minutes, at a temperature of about 28degrees Celsius to form a first solution. In another separate flask,silver nitrate (290.4 grams) was dissolved in water (2.64 liters) andthen isoproply alcohol (22 kilograms) was added to form a secondsolution. The second solution was added to the first solution at anaddition rate of about 180 milliliters per minute. An increase intemperature to about 35 degrees Celsius was noted after the addition.The resultant solution was stirred at 28 degrees Celsius for another 2.5hours. The solution was then heated to reflux. The solution was stirred(stirring rate of 120 revolutions per minute) and maintained at refluxfor a period of about 36 hours.

The resultant solution was spray dried at a temperature of about 100degrees Celsius to remove the solvents to provide a powder with a yieldof over 80 percent, and having an average particle size diameter of lessthan about 10 microns. The spray dried powder was then further processedin two steps, (i) pyrolysis and (ii) calcination. The two step processwas performed to remove the organic components triton X114, ethylacetoacetate, and isopropyl alcohol, without exposing the powder to thetemperature rise equivalent to combustion of the organic components.

For step (i) pyrolysis, the powder was loaded in multiple batches, intotwo quartz boats, in a 6 inch quartz tube, in a 5 feet long tubefurnace. Each boat held approximately 1 kilogram of spray dried powder.20 standard cubic feet per hour of nitrogen (N₂) was fed to the tube.The furnace was then heated following the heating profile: heated to 100degrees Celsius at a rate of 5 degrees Celsius per minute, maintainedfor 3 hours, heated to 550 degrees Celsius at 2 degrees Celsius perminute, maintained for 6 hours, and then the furnace was cooled to 28degrees Celsius at the natural cooling rate of the furnace usingconvection cooling. The heating resulted in either the evaporation ofthe organics, or their decomposition into lighter components orcarbonaceous material. During the pyrolysis process, the powder lostabout 50-55 percent of its mass and roughly 50 percent of its volume.This process was repeated in several batches to pyrolyze all of thespray dried pyrolyzed powder.

The (i) pyrolysis step was followed by a (ii) calcination step in orderto remove any residual carbonaceous material and fully oxidize anyremaining hydroxyls. The pyrolyzed powder was loaded into multiplealumina boats that were stacked in a muffle furnace in air (CM Furnacehaving a capacity around 216 cubic inches). The furnace was heated to600 degrees Celsius at a rate of 1 degree Celsius per minute, andmaintained at this temperature for about 3 hours, followed by coolingthe furnace to 28 degrees Celsius at the natural cooling rate of thefurnace using convection cooling. During the calcination process, thepowder lost approximately about 10 percent of its mass based on thepyrolized powder, resulting in an approximate 60 percent mass loss basedon the original spray dried powder. This process was repeated in severalbatches to calcine the spray dried pyrolyzed powder. The resultantpowder had a surface area of about 336 square meters per gram, a porediameter of about 39.6 Angstorms and a pore volume of about 0.42 cubiccentimeter per gram.

Example 2 Preparation of Monolith Coated with Porous Alumina with Silver

A slurry was prepared in isopropyl alcohol using the porous alumina withsilver prepared in Example 1. The slurry comprised 25 weight percentporous alumina with silver in isopropyl alcohol. The resultant slurrywas mixed in a Planetary Centrifugal Mixer (Thinky, capacity 310 cubiccentimeters) for about 30 seconds and then ultrasonically milled forabout 5 minutes. The slurry turned chocolate milk brown. The slurry waswash coated onto a cordierite monolith having a dimension of 6.23milliliters bulk volume by dip coating. The coated cordierite monolithwas then calcined at 550 degrees Celsius for about 4 hours to obtain awhite colored catalyst comprising silver and alumina wash coated on thecordierite monolith. Weight of porous alumina with silver was 0.81 gramson cordierite monolith initially weighing 3.18 grams.

Assembling the Catalyst Systems in Different Configurations

Base configuration for comparative study: Referring to FIG. 1, acatalyst system 100 for determining the NO_(x) reducing capabilities ofa catalytic composition prepared in Example 2 is provided. The firstcatalytic composition prepared in Example 2 112 was placed in a quartztube 110 having an outer diameter of one inch. The first catalyticcomposition prepared in Example 2 112 was placed inside the quartz tubebetween two plugs of quartz wool 114 and 116. The bulk volume of thecatalytic composition, i.e., the monolith of the first catalyticcomposition 112 prepared in Example 2 was 6.23 milliliters. The weightof the coating of porous alumina with silver (prepared in Example 1) was0.81 grams. The total weight of the monolith and porous alumina withsilver was 3.99 grams. Each plug of quartz wool spanned a length ofabout 0.5 inch along the length of the quartz tube 110 and weighed about0.5 grams. The quartz tube 110 was then placed in a furnace (not shownin FIG. 1). This catalyst system has been used in comparative examplesCE-1 to CE-8 in Table 2 to show the NO_(x) reduction properties of thecatalyst system.

Configuration in accordance with an embodiment of the invention:Referring to FIG. 2, a catalyst system 200 for determining the NO_(x)reducing capabilities of a first catalytic composition prepared inExample 2 in a dual bed configuration with a second catalyticcomposition comprising a commercially purchased copper zeolite or ironzeolite is provided. In this configuration, the first catalyticcomposition prepared in Example 2 212, was placed in a quartz tube 210having an outer diameter of one inch. The first catalytic compositionprepared in Example 2 212 was placed inside the quartz tube between twoplugs of quartz wool 214 and 216. Each plug of quartz wool spanned alength of about 0.5 inch along the length of the quartz tube 210 andweighed about 0.5 grams. A gap of about 1 inch long was left in thequartz tube and again two plugs of quartz wool 218, 220 both about 0.5inch long and 0.5 grams in weight were placed along the length of thequartz tube 210. The second catalytic composition, i.e., copper zeoliteor iron zeolite catalyst 222 was placed between the two plugs of quartzwool 218 and 220. The quartz tube 210 was then placed in a furnace (notshown in FIG. 2). Bulk volume of zeolite monolith used in Examples 3-10was 3.53 milliliters and in Examples 11-18 was 2.96 milliliters. Thiscatalyst system has been used in Examples 3 to 18 (Table 2) to show theNO_(x) reduction properties of the catalyst system.

The catalyst system configurations assembled in the quartz tubes asdescribed in FIG. 1 and FIG. 2, were independently placed in a furnace.In both instances, a simulated exhaust stream 118, and 224, wasdischarged into the quartz tube. The flow of the simulated exhauststream through the quartz tube was at a rate of about 3.2 standardliters per minute. The simulated exhaust stream contained nitric oxide(NO; 300 parts per million), water (7 volume percent based on totalvolumetric flow rate), and oxygen (9 volume percent based on totalvolumetric flow rate). A reductant stream comprising ultra low sulfurdiesel (ULSD) was also discharged into the quartz tube. The ratio of theULSD to NO_(x) was such that the ratio of the carbon atoms in the ULSDwas about 5 to 6 times that of the NO molecules in the stimulatedexhaust stream passed over the catalyst. The ULSD contained less thanabout 15 parts per million sulfur. The gas stream contained 300 partsper million NO. Hence the ratio of carbon:NO of 5:1 translated to about1500 parts per million carbon atoms from the ULSD. In some embodiments,as provided in Table 2 below, during the flow of the simulated exhauststream through the furnace, hydrogen a co-reductant was introduced intothe furnace along with the reductant ULSD. The hydrogen content was 0parts per million in some examples and 1000 parts per million in someexamples as indicated in the Table 2 given below. The temperatures inthe furnace during the experiments were 450, 400, 350 and 300 degreesCelsius. The space velocity (SV) of the simulated exhaust streams, theNO_(x) conversion, and the concentrations of other gases are included inthe Table 2 below.

Comparative examples CE-1 to CE-8 provide data on NO_(x) reduction usinga base configuration described in FIG. 1. Example 3 to Example 6 providedata on NO_(x) reduction using a dual bed catalyst system wherein thefirst bed includes monolith coated with porous alumina described inExample 2 and the second bed includes iron zeolite in the presence of 0parts per million of hydrogen. Example 7 to Example 10 provide data onNO_(x) reduction using a dual bed catalyst system wherein the first bedincludes monolith coated with porous alumina described in Example 2 andthe second bed includes iron zeolite in the presence of 1000 parts permillion of hydrogen. Example 11 to Example 14 provide data on NO_(x)reduction using a dual bed catalyst system wherein the first bedincludes monolith coated with porous alumina described in Example 2 andthe second bed includes copper zeolite in the presence of 0 parts permillion of hydrogen. Example 15 to Example 18 provide data on NO_(x)reduction using a dual bed catalyst system wherein the first bedincludes monolith coated with porous alumina described in Example 2 andthe second bed includes copper zeolite in the presence of 1000 parts permillion of hydrogen.

TABLE 2 Space velocity Space velocity Total space Co- in liters per inliters per velocity in Temperature reductant NO_(x) hour over the hourover the liters per hour in degrees hydrogen conversion Ammonia firstcatalytic second catalytic over the dual Example Celsius in ppm inpercentage in ppm composition composition bed system CE-1 450 0 36.852.6 30000 — 30000 CE-2 400 0 33.8 51.3 30000 — 30000 CE-3 350 0 24.537.1 30000 — 30000 CE-4 300 0 6.8 17.1 30000 — 30000 CE-5 450 1000 36.749.1 30000 — 30000 CE-6 400 1000 42.1 52.8 30000 — 30000 CE-7 350 100039.7 43.6 30000 — 30000 CE-8 300 1000 34.4 30.6 30000 — 30000 Example 3450 0 64.0 2.8 47000 85000 30000 Example 4 400 0 67.0 5.8 47000 8500030000 Example 5 350 0 53.0 8.4 47000 85000 30000 Example 6 300 0 22.05.1 47000 85000 30000 Example 7 450 1000 62.0 2.2 47000 85000 30000Example 8 400 1000 70.0 5.3 47000 85000 30000 Example 9 350 1000 66.09.1 47000 85000 30000 Example 10 300 1000 55.0 8.9 47000 85000 30000Example 11 450 0 64.0 0.8 31000 67000 21000 Example 12 400 0 72.0 1.731000 67000 21000 Example 13 350 0 62.0 6.3 31000 67000 21000 Example 14300 0 28.0 8.7 31000 67000 21000 Example 15 450 1000 65.0 0.7 3100067000 21000 Example 16 400 1000 80.0 1.8 31000 67000 21000 Example 17350 1000 78.0 7.7 31000 67000 21000 Example 18 300 1000 64.0 12.8 3100067000 21000

From the results, it can be seen that the catalyst systems of Examples3-18 including the first catalytic composition comprising a mixture ofthe porous alumina with silver and the second catalytic compositioncomprising copper zeolite or iron zeolite showed superior NO_(x)conversion and lower ammonia slip than the porous alumina with silveralone as shown in comparative examples CE-1 to CE-8. Further whencomparing Examples 3-6 and 11-14 where 0 ppm reductant was employed andExamples 7-10 and 15-18 where 1000 ppm reductant was employed, thecatalyst system provided better NO_(x) conversions in the presence ofco-reductant hydrogen.

Configuration in accordance with an embodiment of the invention:Referring to FIG. 3, a catalyst system 300 for determining the NO_(x)reducing capabilities of a first catalytic composition prepared inExample 2 in a three bed configuration with a second catalyticcomposition comprising a commercially purchased copper zeolite or ironzeolite and a third catalytic composition comprising a DOC is provided.In this configuration, the first catalytic composition prepared inExample 2 312, is placed in a quartz tube 310 having an outer diameterof one inch. The first catalytic composition prepared in Example 2 312is placed inside the quartz tube between two plugs of quartz wool 314and 316. Each plug of quartz wool spanned a length of about 0.5 inchlong along the length of the quartz tube 310 and weighs about 0.5 grams.A gap of about 1 inch long is left in the quartz tube and again twoplugs of quartz wool 318, 320 both about 0.5 inch long and 0.5 grams inweight are placed along the length of the quartz tube 310. The secondcatalytic composition, i.e., copper zeolite or iron zeolite catalyst 322is placed between the two plugs of quartz wool 318 and 320. A gap ofabout 1 inch long is left in the quartz tube and again two plugs ofquartz wool 324, 326 both about 0.5 inch long and 0.5 grams in weightare placed along the length of the quartz tube 310. The third catalyticcomposition, i.e., DOC (Johnson Matthey, DOC) 328 is placed between thetwo quartz plugs 324 and 326. A simulated exhaust stream 330 asdescribed above under 118 and 224, is discharged into the quartz tube.The quartz tube 310 is then placed in a furnace (not shown in FIG. 3).Use of the catalyst system including the first catalytic compositioncomprising a mixture of the homogeneous solid mixture comprising silverand metal inorganic support, the second catalytic composition comprisingcopper zeolite or iron zeolite, and the third catalytic compositioncomprising DOC provides superior NO_(x) conversion and lower ammoniaslip than the porous alumina with silver alone. Further, the three bedcatalyst system provides better NO_(x) conversions in the presence ofco-reductant hydrogen.

As used herein the term “bulk volume” means the volume calculated usingthe outer dimensions of the monolith. As used herein, the term “ammonia(NH₃)-slip” is the amount of ammonia (in ppm of total volumetic flow)that is left after the specified catalyst. This could be after the firstor second bed, depending on how it is described. As used herein the termspace velocity represents the relation between volumetric flow andcatalyst system bed volume. As a matter of definition, the term “diesel”refers to the distillate commonly available to operate in a dieselengine. While those of skill in the art will recognize that diesel fuelmay vary in its precise mixture, that the term diesel encompasses allsuch varieties in mixture commonly available. This may include dieselfuel derived from a variety of sources, including for example,bio-diesel and petro-diesel. Ultra-low Sulfur Diesel refers to specificblends of diesel fuel commonly used in automotive engines that have verylow sulfur levels. Similarly, the term “gasoline” is used to refer toany of the blends of distillate commonly available to operate in agasoline engine.

In still yet another embodiment, is provided an exhaust systemcomprising a fuel delivery system configured to deliver a fuel to anengine; an exhaust stream path configured to receive an exhaust streamfrom the engine; a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a firstcatalytic composition comprising, a homogeneous solid mixture containingsilver and one metal inorganic support; wherein the pores of the solidmixture have an average diameter in a range of about 1 nanometer toabout 15 nanometers; and at least one promoting metal. The catalystsystem further comprises a second catalytic composition comprising, (i)a zeolite, or (ii) a first catalytic material disposed on a firstsubstrate, the first catalytic material comprising an element selectedfrom the group consisting of tungsten, titanium, and vanadium. In oneembodiment, the reductant delivery system further comprises aco-reductant.

Referring to FIG. 4, an exhaust system 400 capable of reducing NO_(x) isprovided. The exhaust system 400 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system 410 mayalso comprise a reductant delivery system 424 configured to deliver areductant. In one embodiment, the reductant is the fuel 414. In oneembodiment, the reductant comprising the fuel 414 is directly deliveredto the catalyst system 420 from the fuel tank 412 via an injector orvaporizer or burner 426 through the point of injection 428. In oneembodiment, a portion of the fuel 414 may be delivered to the catalystsystem 420 by the exhaust stream 418 from the fuel tank 412 via aninjector or vaporizer or burner 430 through the point of injection 432.In one embodiment, the reductant delivery system 424 further comprises aco-reductant 434. In one embodiment, the co-reductant 434 may begenerated by passing the fuel 414 through a reformer 436. A source ofoxygen 438 is provided to the reformer 436. In one embodiment, theco-reductant 434 generated by the reformer 436 includes a syn-gascomprising hydrogen and carbon monoxide. The co-reductant 434 is passedthrough the catalyst system 420 through the point of injection 428. Inone embodiment, a diesel particulate filter DPF 440 is located betweenthe engine 416 and the catalyst system 420 before the point of injection428. In this embodiment, the reductant comprising the fuel 414 and theco-reductant 434 are delivered to the catalyst system 420 through thepoint of injection 428 after the exhaust stream 418 is passed throughthe DPF 440. In one embodiment, a burner 442 is provided between thefuel tank 412 and the catalyst system 420. The burner 442 burns the fuel414 to increase the temperature of the exhaust stream 418 which can beused to improve the performance of the catalyst system 420 in situationswhere the exhaust stream 420 has a temperature which is below theoptimum operating conditions of the catalyst system 422. In thisembodiment, the output of the burner 444 may be located between the DPF440 and the point of injection 428 of the reductant comprising the fuel414 and the co-reductant 434 in the exhaust stream 418.

In an exemplary embodiment as shown in FIG. 4, the fuel may compriseULSD. In certain embodiments as shown in FIG. 4, the reductant comprisesthe fuel. In certain embodiments wherein the reductant is not the sameas the fuel, a separate reductant tank can be used to contain thereductant as will be explained in the description of figures providedbelow. In embodiments, where the reductant is not the fuel, thereductants may include ethanol, gasoline, mixture of ethanol andgasoline, and mixture of ethanol and diesel. The engine 416 can be anyform of internal combustion engine, which produces exhaust(reciprocating or rotating) and can operate on a variety of fuel sourcesincluding gas, biodiesel, diesel, and natural gas. The DPF is anoptional equipment that may be located up stream of the catalyst systemas shown in FIG. 4 or down-stream as will be explained in the figuredescriptions given below. The purpose of the filter is to removeparticulate mater (soot and ash) from the exhaust stream. In certainembodiments (not shown in figure), the DPF may be paired with a dieselinjector to regenerate the DPF by burning off soot. The burner asdescribed above burns diesel fuel to increase the temperature of theexhaust stream which can be used to improve the performance of thecatalyst in situation where the exhaust temperature is below the optimumoperating conditions of the catalyst. The burner is placed upstream ofthe diesel and the reformer injection which is just before the catalystsystem. In the case where DPF is upstream of the catalyst system theburner may be upstream or downstream of DPF. The reformer generates theco-reductant hydrogen from the diesel fuel and oxygen source (mostlikely from air). Carbon monoxide, carbon dioxide and water, can also begenerated in the reforming process. The reformer may also perform watergas shift reaction to increase yield of hydrogen. The injector orvaporizer or burner is the means by which the reductant, for example,diesel fuel, is delivered to the catalyst. The reductant can either bevaporized and delivered as a gas stream or be atomized or sprayed intothe exhaust (or onto the catalyst system) with an injector. The catalystsystem 420 may include the catalyst system configurations describedherein above in the example section. Additionally the exhaust system mayinclude other equipments such as pumps, valves, sensors, control loops,computers (control logic), storage tanks, mixers (gas or liquid),insulation, flow paths, separators, etc. as would be appreciated by oneskilled in the art.

Referring to FIG. 5, an exhaust system 500 capable of reducing NO_(x) isprovided. The exhaust system 500 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system 410 mayalso comprise a reductant delivery system 424 configured to deliver areductant. The reductant delivery system 424 comprises a fuelfractionator 510 and an injector or vaporizer or burner 426. In oneembodiment, the reductant comprising the fuel 414 is first passedthrough the fuel fractionator 510 to provide a light fuel fraction 512and a heavy fuel fraction 514. The light fuel fraction 512 compriseshydrocarbons having an average carbon chain length of less than about 12carbons and the heavy fuel fraction 514 comprises hydrocarbons having anaverage carbon chain length of greater than about 12 carbons. The lightfuel fraction 512 is delivered to the catalyst system 420 from the fueltank 412 via an injector or vaporizer or burner 426 through the point ofinjection 428. In one embodiment, a portion of the fuel 414 may bedelivered to the catalyst system 420 by the exhaust stream 418 from thefuel tank 412 via an injector or vaporizer or burner 430 through thepoint of injection 432. The heavy fuel fraction 514 is delivered to theengine 416 through the fuel 414. In one embodiment, the reductantdelivery system 424 further comprises a co-reductant 434. In oneembodiment, the co-reductant 434 may be generated by passing the fuel414 through a reformer 436. A source of oxygen 438 is provided to thereformer 436. In one embodiment, the co-reductant 434 generated by thereformer 436 includes a syn-gas comprising hydrogen and carbon monoxide.The co-reductant 434 is passed through the catalyst system 420 throughthe point of injection 428. In one embodiment, a DPF 440 is locatedbetween the engine 416 and the catalyst system 420 before the point ofinjection 428. In this embodiment, the reductant comprising the lightfuel fraction 512 and the co-reductant 434 are delivered to the catalystsystem 420 after the exhaust stream 418 is passed through the DPF 440through the point of injection 428. In one embodiment, a burner 442 isprovided between the fuel tank 412 and the catalyst system 420. Theburner 442 burns the fuel 414 to increase the temperature of the exhauststream 418 which can be used to improve the performance of the catalystsystem 420 in situations where the exhaust stream 418 has a temperaturewhich is below the optimum operating conditions of the catalyst system420. In this embodiment, the output of the burner 444 may be locatedbetween the DPF 440 and the point of injection 428 of the reductantcomprising the light fuel fraction 512 and the co-reductant 434 in theexhaust stream 418.

Referring to FIG. 6, an exhaust system 600 capable of reducing NO_(x) isprovided. The exhaust system 600 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system may alsocomprise a reductant delivery system 424 configured to deliver areductant. In one embodiment, the reductant is the fuel 414. In oneembodiment, the reductant comprising the fuel 414 is directly deliveredto the catalyst system 420 from the fuel tank 412 via an injector orvaporizer or burner 426 through the point of injection 428. In oneembodiment, a portion of the fuel 414 may be delivered to the catalystsystem 420 by the exhaust stream 418 from the fuel tank 412 via aninjector or vaporizer or burner 430 through the point of injection 432.In one embodiment, the reductant delivery system 424 further comprises aco-reductant 434. In one embodiment, the co-reductant 434 may begenerated by passing the fuel 414 through a reformer 436. A source ofoxygen 438 is provided to the reformer 436. In one embodiment, theco-reductant 434 generated by the reformer 436 includes a syn-gascomprising hydrogen and carbon monoxide. The co-reductant 434 is passedthrough the catalyst system 420 through the point of injection 432. Inone embodiment, a DPF 440 is located after the catalyst system 420 andthe exhaust stream 418 is passed through the catalyst system 420 and theDPF 440 before exiting as the treated exhaust stream 422. In thisembodiment, the reductant comprising the fuel 414 is delivered to theexhaust stream 418 through the point of injection 428. In oneembodiment, a burner 442 is provided between the fuel tank 412 and thecatalyst system 420. The burner 442 burns the fuel 414 to increase thetemperature of the exhaust stream 418 which can be used to improve theperformance of the catalyst system 420 in situations where the exhauststream 418 has a temperature which is below the optimum operatingconditions of the catalyst system 420. In this embodiment, the output ofthe burner 444 is connected in the exhaust stream between the engine 418and the point of injection 432 of the reductant comprising the fuel 414and the co-reductant 434 in the exhaust stream 418.

Referring to FIG. 7, an exhaust system 700 capable of reducing NO_(x) isprovided. The exhaust system 700 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system may alsocomprise a reductant delivery system 424 configured to deliver areductant. The reductant delivery system 424 comprises a fuelfractionator 510 and an injector or vaporizer or burner 426. In oneembodiment, the reductant comprising the fuel 414 is first passedthrough the fuel fractionator 710 to provide a light fuel fraction 712and a heavy fuel fraction 714. The light fuel fraction 712 compriseshydrocarbons having an average carbon chain length of less than about 12carbons and the heavy fuel fraction 714 comprises hydrocarbons having anaverage carbon chain length of greater than about 12 carbons. The lightfuel fraction 712 is delivered to the catalyst system 420 from the fueltank 412 via an injector or vaporizer or burner 426 through the point ofinjection 428. In one embodiment, a portion of the fuel 414 may bedelivered to the catalyst system 420 by the exhaust stream 418 from thefuel tank 412 via an injector or vaporizer or burner 430 through thepoint of injection 432. The heavy fuel fraction 714 is delivered to theengine 416 through the fuel 414. In one embodiment, the reductantdelivery system 424 further comprises a co-reductant 434. In oneembodiment, the co-reductant 434 may be generated by passing the fuel414 through a reformer 436. A source of oxygen 438 is provided to thereformer 436. In one embodiment, the co-reductant 434 generated by thereformer 436 includes a syn-gas comprising hydrogen and carbon monoxide.The co-reductant 434 is passed through the catalyst system 420 throughthe point of injection 432. In one embodiment, a DPF 440 is locatedafter the catalyst system 420 and exhaust stream 418 is passed throughthe catalyst system 420 and the DPF 440 before exiting as the treatedexhaust stream 422. In this embodiment, the reductant comprising thelight fuel fraction 712 and the co-reductant 434 are delivered to theexhaust stream 418 through the point of injection 428. In oneembodiment, a burner 442 is provided between the fuel tank 412 and thecatalyst system 420. The burner 442 burns the fuel 414 to increase thetemperature of the exhaust stream 418 which can be used to improve theperformance of the catalyst system 420 in situations where the exhauststream 418 has a temperature which is below the optimum operatingconditions of the catalyst system 420. In this embodiment, the output ofthe burner 444 is connected in the exhaust stream between the engine 416and the point of injection 432 of the reductant comprising fuel 414 andthe co-reductant 434 in the exhaust stream 418.

Referring to FIG. 8, an exhaust system 800 capable of reducing NO_(x) isprovided. The exhaust system 800 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system may alsocomprise a reductant delivery system 424 configured to deliver areductant. In one embodiment, the reductant is not the same as the fuel.In this embodiment, a reductant tank 810 is provided to deliver thereductant 812 to the catalyst system 422 via the injector or vaporizeror burner 426 to the point of injection 428. In one embodiment, aportion of the fuel 414 may be delivered to the catalyst system 420 bythe exhaust stream 418 from the fuel tank 412 via an injector orvaporizer or burner 430 through the point of injection 432. In oneembodiment, the reductant delivery system 424 further comprises aco-reductant 434. In one embodiment, the co-reductant 434 may begenerated by passing the fuel 414 through a reformer 436. A source ofoxygen 438 is provided to the reformer 436. In one embodiment, theco-reductant 434 generated by the reformer 436 includes a syn-gascomprising hydrogen and carbon monoxide. The co-reductant 434 is passedthrough the catalyst system 420 through the point of injection 428. Inone embodiment, a DPF 440 is located between the engine 416 and thecatalyst system 420 before the point of injection 428. In thisembodiment, the reductant 812 and the co-reductant 434 are delivered tothe catalyst system 420 through the point of injection 428 after theexhaust stream 418 is passed through the DPF 440. In one embodiment, aburner 442 is provided between the fuel tank 412 and the catalyst system420. The burner 442 burns the fuel 414 to increase the temperature ofthe exhaust stream 418 which can be used to improve the performance ofthe catalyst system 420 in situations where the exhaust stream 418 has atemperature which is below the optimum operating conditions of thecatalyst system 420. In this embodiment, the output of the burner 444may be located between the DPF 440 and the point of injection 428 of thereductant 812 and the co-reductant 434 in the exhaust stream 418.

Referring to FIG. 9, an exhaust system 900 capable of reducing NO_(x) isprovided. The exhaust system 900 comprises a fuel delivery system 410which is configured to deliver a fuel 414 contained in a fuel tank 412to an engine 416. An exhaust stream 418 is generated by the engine 416and this exhaust stream 418 is passed through a catalyst system 420 toprovide a treated exhaust stream 422. The fuel delivery system may alsocomprise a reductant delivery system 424 configured to deliver areductant. In one embodiment, the reductant is not the same as the fuel.In this embodiment, a reductant tank 910 is provided to deliver thereductant 912 to the exhaust stream 418 from the reductant tank 910 viaan injector or vaporizer or burner 430 and the exhaust stream 418carries the reductant 912 to the catalyst system 420 through the pointof injection 432. In one embodiment, a portion of the fuel 414 isdelivered to the catalyst system 420 from the fuel tank 412 via aninjector or vaporizer or burner 426 through the point of injection 428.In one embodiment, the reductant delivery system 424 further comprises aco-reductant 434. In one embodiment, the co-reductant 434 may begenerated by passing the fuel 414 through a reformer 436. A source ofoxygen 438 is provided to the reformer 436. In one embodiment, theco-reductant 434 generated by the reformer 436 includes a syn-gascomprising hydrogen and carbon monoxide. The co-reductant 434 is passedthrough the catalyst system 420 through the point of injection 432. Inone embodiment, a DPF 440 is located after the catalyst system 420 andexhaust stream 418 is passed through the catalyst system 420 and the DPF440 before exiting as the treated exhaust stream 422. In thisembodiment, the reductant comprising the fuel 414 is delivered to theexhaust stream 418 through the point of injection 428 which lies betweenthe catalyst system 420 and the DPF 440. In one embodiment, a burner 442is provided between the fuel tank 412 and the catalyst system 420. Theburner 442 burns the fuel 414 to increase the temperature of the exhauststream 418 which can be used to improve the performance of the catalystsystem 420 in situations where the exhaust stream 418 has a temperaturewhich is below the optimum operating conditions of the catalyst system420. In this embodiment, the output of the burner 444 is connected inthe exhaust stream between the engine 418 and the point of injection 432of the reductant 912 and the co-reductant 434 in the exhaust stream 418.

In still yet another embodiment is provided an exhaust system comprisinga fuel delivery system configured to deliver a fuel to an engine; anexhaust stream path configured to receive an exhaust stream from theengine; and a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a homogeneoussolid mixture containing silver and one metal inorganic support; whereinthe pores of the solid mixture have an average diameter in a range ofabout 1 nanometer to about 15 nanometers; and at least one promotingmetal. The catalyst system further comprises a second catalyticcomposition comprising, (i) a zeolite, or (ii) a first catalyticmaterial disposed on a first substrate, the first catalytic materialcomprising an element selected from the group consisting of tungsten,titanium, and vanadium. The catalyst further comprises a third catalyticcomposition disposed downstream from the second catalytic composition;the third catalytic composition comprising a second catalytic materialdisposed on a second substrate, wherein the second catalytic material isselected from the group consisting of platinum, palladium, ruthenium,rubidium, osmium, and iridium. In one embodiment, the reductant deliverysystem further comprises a co-reductant.

In still yet another embodiment is provided an exhaust system comprisinga fuel delivery system configured to deliver a fuel to an engine; anexhaust stream path configured to receive an exhaust stream from theengine; and a reductant delivery system configured to deliver areductant to the exhaust stream path; and a catalyst system disposed inthe exhaust stream path. The catalyst system comprises: a firstcatalytic composition comprising, a first catalytic material comprisingsilver disposed on a first substrate, and at least one promoting metal.The catalyst system further comprises a second catalytic compositioncomprising, (i) a zeolite, or (ii) a second catalytic material disposedon a second substrate, the second catalytic material comprising anelement selected from the group consisting of tungsten, titanium, andvanadium. The catalyst further comprises a third catalytic compositiondisposed downstream from the second catalytic composition; the thirdcatalytic composition comprising a third catalytic material disposed ona third substrate, wherein the third catalytic material is selected fromthe group consisting of platinum, palladium, ruthenium, rubidium,osmium, and iridium. In one embodiment, the reductant delivery systemfurther comprises a co-reductant.

While the systems and techniques herein have been described withreference to exemplary embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from theiressential scope. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of a given embodimentwithout departing from the essential scope thereof. Therefore, it isintended that these systems and techniques are not limited to theparticular embodiments disclosed as the best mode contemplated forcarrying them out.

The various embodiments described herein may be examples of catalyticcompositions and systems using such compositions and techniques formanufacturing these embodiments. Any given embodiment may provide one ormore of the advantages recited, but need not provide all objects oradvantages recited for any other embodiment. Those skilled in the artwill recognize that the systems and techniques described herein may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

This written description may enable those of ordinary skill in the artto make and use embodiments having alternative elements that likewisecorrespond to the elements recited herein. While only certain featuresand embodiments have been illustrated and described herein, manymodifications and changes may occur to one of ordinary skill in therelevant art. Thus, it is intended that the scope of the inventiondisclosed should not be limited by the particular disclosed embodimentsdescribed above, but should be determined only by a fair reading of theclaims that follow.

1. A catalyst system comprising: a first catalytic compositioncomprising; a homogeneous solid mixture containing at least onecatalytic metal and at least one metal inorganic support; wherein thepores of the solid mixture have an average diameter in a range of about1 nanometer to about 15 nanometers; and at least one promoting metal;and a second catalytic composition comprising; (i) a zeolite, or (ii) afirst catalytic material disposed on a first substrate, the firstcatalytic material comprising an element selected from the groupconsisting of tungsten, titanium, and vanadium.
 2. The catalyst systemof claim 1, wherein the catalytic metal comprises alkali metals,alkaline earth metals, transition metals, or a combination thereof. 3.The catalyst system of claim 1, wherein the catalytic metal comprisessilver, platinum, gold, palladium, iron, nickel, cobalt, gallium,indium, ruthenium, rhodium, osmium, iridium, or combinations of at leasttwo of the foregoing metals.
 4. The catalyst system of claim 1, whereinthe catalytic metal comprises silver.
 5. The catalyst system of claim 1,wherein the metal inorganic support comprises alumina.
 6. The catalystsystem of claim 1, wherein the at least one promoting metal is selectedfrom the group consisting of gallium, indium, gold, vanadium, zinc, tin,bismuth, cobalt, molybdenum, and tungsten.
 7. The catalyst system ofclaim 1, wherein the zeolite comprises zeolite Y, zeolite beta,mordenite, ferrierite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35,ZSM-38, ZSM-48, ZSM-50, ZSM-57, zeolite A, zeolite X, or a combinationcomprising at least two of the foregoing zeolites.
 8. The catalystsystem of claim 1, wherein the zeolite comprises zeolite Y, zeolitebeta, mordenite, ferrierite, ZSM-5, or a combination comprising at leasttwo of the foregoing zeolites.
 9. The catalyst system of claim 1,wherein the first substrate comprises at least one member selected fromthe group consisting of alumina, titania, zirconia, ceria, siliconcarbide and mixtures thereof.
 10. The catalyst system of claim 1,further comprising a third catalytic composition disposed downstreamfrom the second catalytic composition; the third catalytic compositioncomprising a second catalytic material disposed on a second substrate,wherein the second catalytic material is selected from the groupconsisting of platinum, palladium, ruthenium, rhodium, osmium, andiridium.
 11. The catalyst system of claim 10, wherein the secondsubstrate comprises at least one member selected from the groupconsisting of alumina, titania, zirconia, ceria, silicon carbide andmixtures thereof.
 12. The catalyst system of claim 1, further comprisinga delivery system configured to deliver a reductant.
 13. The catalystsystem of claim 12, wherein the reductant is a hydrocarbon.
 14. Thecatalyst system of claim 13, wherein the hydrocarbon has an averagecarbon chain length in a range of about 2 carbon atoms to about 24carbon atoms.
 15. The catalyst system of claim 12, wherein the reductantis one or more of diesel, ultra-low sulfur diesel, ethanol, gasoline,and octane.
 16. The catalyst system of claim 12, wherein the reductantis an oxygenated hydrocarbon.
 17. The catalyst system of claim 16,wherein the reductant is ethanol.
 18. The catalyst system of claim 12,wherein the reductant is diesel.
 19. The catalyst system of claim 12,wherein the delivery system further comprises a co-reductant.
 20. Thecatalyst system of claim 19, wherein the co-reductant is hydrogen.
 21. Acatalyst system comprising: a first catalytic composition comprising; ahomogeneous solid mixture containing at least one catalytic metal and atleast one metal inorganic support; wherein the pores of the solidmixture have an average diameter in a range of about 1 nanometer toabout 15 nanometers; and at least one promoting metal; a secondcatalytic composition comprising; (i) a zeolite, or (ii) a firstcatalytic material disposed on a first substrate, the first catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium; and a third catalytic compositiondisposed downstream from the second catalytic composition, the thirdcatalytic composition comprising; a second catalytic material disposedon a second substrate, wherein the second catalytic material is selectedfrom the group consisting of platinum, palladium, ruthenium, rubidium,osmium, and iridium.
 22. The catalyst system of claim 21, wherein thecatalytic metal comprises alkali metals, alkaline earth metals,transition metals, or a combination thereof.
 23. The catalyst system ofclaim 21, wherein the metal inorganic support comprises alumina.
 24. Thecatalyst system of claim 21, wherein the at least one promoting metal isselected from the group consisting of gallium, indium, gold, vanadium,zinc, tin, bismuth, cobalt, molybdenum, and tungsten.
 25. The catalystsystem of claim 21, Wherein the zeolite comprises zeolite Y, zeolitebeta, mordenite, ferrierite, ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34,ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, zeolite A, zeolite X or acombination comprising at least two of the foregoing zeolites.
 26. Thecatalyst system of claim 21, further comprising a delivery systemconfigured to deliver a reductant.
 27. The catalyst system of claim 26,wherein the delivery system further comprises a co-reductant.
 28. Acatalyst system comprising: a first catalytic composition comprising; afirst catalytic material comprising silver disposed on a firstsubstrate; and at least one promoting metal; a second catalyticcomposition comprising; (i) a zeolite, or (ii) a second catalyticmaterial disposed on a second substrate, the second catalytic materialcomprising an element selected from the group consisting of tungsten,titanium, and vanadium; and a third catalytic composition disposeddownstream from the second catalytic composition, the third catalyticcomposition comprising; a third catalytic material disposed on a thirdsubstrate, wherein the third catalytic material is selected from thegroup consisting of platinum, palladium, ruthenium, rubidium, osmium,and iridium.
 29. The catalyst system of claim 28, wherein the at leastone promoting metal is selected from the group consisting of gallium,indium, gold, vanadium, zinc, tin, bismuth, cobalt, molybdenum, andtungsten.
 30. The catalyst system of claim 28, wherein the zeolitecomprises zeolite Y, zeolite beta, mordenite, ferrierite, ZSM-5, ZSM-12,ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, zeoliteA, zeolite X or a combination comprising at least two of the foregoingzeolites.
 31. The catalyst system of claim 28, wherein the firstsubstrate, the second substrate, and the third substrate independentlycomprise at least one member selected from the group consisting ofalumina, titania, zirconia, ceria, silicon carbide and mixtures thereof.32. The catalyst system of claim 28, further comprising a deliverysystem configured to deliver a reductant.
 33. The catalyst system ofclaim 32, wherein the delivery system further comprises a co-reductant.34. An exhaust system comprising: a fuel delivery system configured todeliver a fuel to an engine; an exhaust stream path configured toreceive an exhaust stream from the engine; a reductant delivery systemconfigured to deliver a reductant to the exhaust stream path; and acatalyst system disposed in the exhaust stream path, wherein thecatalyst system comprises: a first catalytic composition comprising; ahomogeneous solid mixture containing at least one catalytic metal and atleast one metal inorganic support; wherein the pores of the solidmixture have an average diameter in a range of about 1 nanometer toabout 15 nanometers; and at least one promoting metal; and a secondcatalytic composition comprising; (i) a zeolite, or (ii) a firstcatalytic material disposed on a first substrate, the first catalyticmaterial comprising an element selected from the group consisting oftungsten, titanium, and vanadium.
 35. The exhaust system of claim 34,wherein the reductant is a hydrocarbon.
 36. The exhaust system of claim35, wherein the hydrocarbon has an average carbon chain length in therange of about 2 carbon atoms to about 24 carbon atoms.
 37. The exhaustsystem of claim 34, wherein the reductant is one or more of diesel,ultra-low sulfur diesel, ethanol, gasoline, and octane.
 38. The exhaustsystem of claim 34, wherein the reductant is an oxygenated hydrocarbon.39. The exhaust system of claim 38, wherein the reductant is ethanol.40. The exhaust system of claim 34, wherein the reductant is diesel. 41.The exhaust system of claim 34, wherein the delivery system furthercomprises a co-reductant.
 42. The exhaust system of claim 41, whereinthe co-reductant is hydrogen.
 43. An exhaust system comprising: a fueldelivery system configured to deliver a fuel to an engine; an exhauststream path configured to receive an exhaust stream from the engine; areductant delivery system configured to deliver a reductant to theexhaust stream path; and a catalyst system disposed in the exhauststream path, wherein the catalyst system comprises: a first catalyticcomposition comprising; a homogeneous solid mixture containing at leastone catalytic metal and at least one metal inorganic support; whereinthe pores of the solid mixture have an average diameter in a range ofabout 1 nanometer to about 15 nanometers; and at least one promotingmetal; a second catalytic composition comprising; (i) a zeolite, or (ii)a first catalytic material disposed on a first substrate, the firstcatalytic material comprising an element selected from the groupconsisting of tungsten, titanium, and vanadium; and a third catalyticcomposition disposed downstream from the second catalytic composition;the third catalytic composition comprising; a second catalytic materialdisposed on a second substrate, wherein the second catalytic material isselected from the group consisting of platinum, palladium, ruthenium,rubidium, osmium, and iridium.
 44. The exhaust system of claim 43,wherein the reductant delivery system further comprises a co-reductant.45. An exhaust system comprising: a fuel delivery system configured todeliver a fuel to an engine; an exhaust stream path configured toreceive an exhaust stream from the engine; a reductant delivery systemconfigured to deliver a reductant to the exhaust stream path; and acatalyst system disposed in the exhaust stream path, wherein thecatalyst system comprises: a first catalytic composition comprising; afirst catalytic material disposed on a first substrate; and at least onepromoting metal; a second catalytic composition comprising; (i) azeolite, or (ii) a second catalytic material disposed on a secondsubstrate, the second catalytic material comprising an element selectedfrom the group consisting of tungsten, titanium, and vanadium; and athird catalytic composition disposed downstream from the secondcatalytic composition; the third catalytic composition comprising; athird catalytic material disposed on a third substrate, wherein thethird catalytic material is selected from the group consisting ofplatinum, palladium, ruthenium, rubidium, osmium, and iridium.
 46. Theexhaust system of claim 45, wherein the reductant delivery systemfurther comprises a co-reductant.